Filter device, especially air filter for an internal combustion engine

ABSTRACT

A filter device comprises a filter element that is comprised of at least two radially nested filter bellows, wherein at least one filter bellows is to be flown through in the radial direction and a flow space for the fluid is formed between the filter bellows. Each filter bellows is embodied as a star-shaped filter with filter folds arranged in a star shape. On at least one end face of the filter element a sealing ring is arranged between a filter bellows and the filter housing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. Ser. No. 12/589,527 filedFeb. 26, 2009 which claims priority to International Application No.PCT/EP2009/052315 filed Feb. 26, 2009 designating the U.S. U.S. Ser. No.12/589,527 further claims a priority date of Feb. 26, 2008 based onprior filed German patent application No. 10 2008 011 186.4, the entirecontents of the aforesaid U.S. Ser. No. 12/589,527, 10 2008 011 186.4and PCT/EP2009/052315 being incorporated herein by reference.

TECHNICAL FIELD

The invention concerns a filter device, especially an air filter for aninternal combustion engine.

PRIOR ART

For example, EP 1 364 695 A1 discloses an air filter that is integratedinto the intake manifold of an internal combustion engine in order tosubject the combustion air to be supplied to the cylinders of theinternal combustion engine to a filtration action. The air filter issubstantially of a three-part configuration and comprises a filterelement that is configured as an exchangeable filter cartridge throughwhich the combustion air flows axially and that is insertable radiallyby means of a closable lid into the filter housing. The filter cartridgehas arranged upstream thereof a cyclone preseparator that serves forseparation of coarse dirt particles. Downstream of the filter cartridgethere is a secondary or fine filter element that also is insertableradially into the filter housing when the lid is open. Cyclonepreseparator, filter cartridge, and fine filter element are positionedaxially sequentially behind one another and the combustion air to befiltered passes through them without deflection in the axial direction.

As a main filter element that is received in the filter cartridge, forexample, wound filters are suitable that are comprised of a corrugatedfilter material that is wound about a core, wherein as a result of thecorrugation axial flow passages are formed by the filter element thatare closed of alternatingly at the end faces. Such a filter element is,for example, disclosed in U.S. Pat. No. 7,008,467 B2.

Also known are filter elements that are comprised of a star-shapedfolded filter element in the form of a filter bellows whose filter foldsextend in radial direction wherein the front edges of the filter foldsextend in axial direction.

A filter element of a different configuration that is also suitable forair filtration is disclosed in FR 1 288 229. The filter element iscomprised of two radially nested filter bellows or star-shaped filterswith filter folds that are arranged in a star-shape and between which aflow space for the axial outflow of the filtered fluid is arranged. Theinner side of the radially inwardly positioned filter bellows as well asthe outer side of the radially outwardly positioned filter bellows eachform the unfiltered side by means of which intake of the fluid to befiltered is realized radially through the filter element. Theintermediately positioned flow space serves for axial outflow of thefilter fluid.

SUMMARY OF THE INVENTION

The invention has the object to provide with simple constructivemeasures a filter device that is characterized by a high filtrationefficiency wherein the filter device should be designed to be servicedwith minimal expenditure.

This object is solved according to the invention with the features ofthe independent claims. The dependent claims provide expedient furtherembodiments.

According to a first solution of the invention the filter devicecomprises a filter element in a filter housing that is configured as amulti-bellows filter, in particular as a double-bellows filter, with atleast two radially nested filter bellows between which a flow space forthe fluid is formed, wherein the flow space communicates with an endface of the filter element. Each filter bellows is configured as astar-shaped filter with filter folds arranged in a star shape andextending in the radial direction and having axially extending frontedges. The radially inwardly positioned front edges of the folds of theouter filter bellows as well as the radially outwardly positioned frontedges of the folds of the inwardly positioned filter bellows delimit theflow space, respectively, that serves expediently for outflow of thefiltered fluid, optionally also for intake of the unfiltered fluid.

Moreover, on at least one end face of the filter element a sealing ringis arranged which is located between the filter bellows and the filterhousing. The sealing ring serves in particular for fluid-tightseparation of the unfiltered side from the filtered side of the filterelement and prevents thus leakage flows that would impair the efficiencyof the filter device. The sealing ring is expediently clamped axiallybetween the filter element and the inner side of the housing and isforce-loaded in the axial direction. Basically, a radial force loadingor a combination of axial and radial loading is also suitable. Moreover,the sealing ring is advantageously arranged at the radial outer side ofthe filter element, in particular at a transition between axial end faceand radially outwardly positioned wall surface of the filter element.This embodiment enables intake of at least a partial flow of the fluidto be filtered via the radially outwardly positioned wall surface of thefilter element and passage for filtration radially through the filterelement until it reaches the flow space between the two filter bellows.In this embodiment, the sealing ring delimits at the same time theannular space between the inner side of the housing and the outer wallsurface of the sealing element in the axial direction.

Intake to the filter element embodied as a multi-bellows filter as wellas outflow of the filtered fluid can be carried out in different ways.On the one hand, it is possible to enable flow through the wall of eachfilter bellows exclusively in radial direction and to remove thefiltered fluid exclusively axially through the flow space thatconstitutes at the same time the clean chamber. Moreover, mixed formsare possible also, for example, in such a way that at least one bellows,in addition to the radial flow, also has axial intake and, likewise, theoutflow of at least one bellows, in addition to flow being guidedthrough the flow space in the axial direction, is realized also by flowpassages within a bellows. Advantageously, the axial intake is howeverrealized through flow passages of the first filter bellows, for example,of the outwardly positioned filter bellows, and the axial outflow isrealized through flow passages of the second filter bellows, forexample, of the radially inwardly positioned filter bellows. In order toachieve intake and outflow in the desired way, cover elements areexpediently provided, in particular cover disks or cover rings on thecorresponding axial end faces of the filter bellows. For example, theaxial end face of the radially inwardly positioned filter bellows at theintake side of the filter element is covered by a cover ring so that atthis location an axial intake is prevented. The axial end face in theintake area of the radially outwardly positioned filter bellows howevercan be open in order to enable at this location also axial intake inaddition to radial intake.

At the outflow side of the filter bellows, there is advantageously acover disk that closes off the inwardly positioned intake space withinthe filter bellows in the axial direction in order to prevent leakageimmediately between the unfiltered side and the filtered side. The axialend face of the inner filter bellows however can remain without a coverso that through it an axial outflow is possible in principle. At thesame time, the axial end face in the outflow area of the radiallyoutwardly positioned filter bellows is covered by a cover ring whichprevents axial outflow at this location.

Moreover, it is expedient to tack two immediately neighboring filterfolds together on an axial end face of a filter bellows, in particularto adhesively connect them or glue them together. Advantageously, thisis done for each filter bellows such that only at one axial end tackingof the front edges of the filter folds is performed while the frontedges of the filter folds at the opposed end face are covered by a coverelement. Relative to the two filter bellows, the tacking of the frontedges of the filter folds and covering are performed alternatingly sothat, for example, on the radially outwardly positioned filter bellowsthe front edges are adhesively connected and on the opposite axial endface they are covered by a cover ring and on the radially inwardlypositioned filter bellows the axial intake side is covered by a coverdisk and the front edges at the opposite axial outflow side are tackedtogether. By tacking the front edges flow spaces or passages areproduced in the axial direction wherein by interaction with the coverelements it is ensured that the supplied fluid must flow through thefilter wall in the radial direction.

The filter bellows are preferably configured as star-shaped filters. Itcan also be expedient not to provide a star-shaped folding but a foldingin the axial direction with fold edges that extend in thecircumferential direction or at least have a component extending in thecircumferential direction. Such filter bellows with a bellows action inthe axial direction can be provided with or without folds arranged in astar shape. Optionally, there is also the possibility of folding in astar shape and folding in the axial direction.

The filter bellows are preferably designed as individual bellows thatare radially nested and concentrically arranged relative to one another.According to one embodiment, it is also possible to form two oroptionally even more filter bellows from a single contiguous bellows inthat at one or several locations of the single bellows a section is bentwherein the bending edge forms an axial front edge of the intake oroutflow side of the filter element.

Moreover, it is possible to design the filter bellows to be identicalwith identical configuration across axial length or to be different.Possible is a cylindrical shape as well as a conical shape of a filterbellows or of both filter bellows. According to an advantageousembodiment it is provided that the radially outwardly positioned filterbellows has a cylinder shape whose outer diameter and inner diameter donot change across the axial length and that the radially inwardlypositioned filter bellows has a cone shape wherein the cone expedientlytapers from the intake side to the outflow side. In this way, a flowspace between the filter bellows is produced in the form of an annularcone that widens toward the outflow side; this may be advantageous inregard to fluidic considerations with regard to outflow of the filteredfluid. Across the axial length the flow space has thus a changingcross-section wherein the rate of change is constant. Basically, also avarying rate of change is possible across the axial length. Moreover,the flow space can also have identical cross-section which is the casewhen the inner side of the outer filter bellows and the outer side ofthe inner filter bellows are positioned concentrically to one another.

Moreover, it can be advantageous to provide between the filter bellows asupport frame which frames the flow space between the filter bellows. Inparticular, for large volume filtering devices whose filter elementshave a correspondingly higher weight, the support frame that ispreferably comprised of synthetic material and expediently compriseswebs extending in the axial direction as well as in the circumferentialdirection increases the stability.

According to a further aspect of the invention, the filter device has afilter element in the filter housing which filter element is comprisedof a continuous filter web with a plurality of parallel filter layersthat are connected to one another by curved connecting sections of thefilter web wherein between neighboring filter layers spacers areprovided and the intermediate spaces between the neighboring filterlayers provide flow spaces for the fluid. The filter layers are planaror flat; accordingly, the intermediately positioned flow spaces are thusdelimited by parallel planes. By means of the curved connecting sectionsof the filter web that delimit alternatingly neighboring flow spaces atthe opposite end faces of the filter elements, it is ensured that everyother flow space at the intake side is open or closed. The fluid to befiltered is introduced axially into the open flow spaces and must passin the flow space radially the delimiting filter wall because theopposite axial end face of this flow space is closed off at the outflowside by the curved connecting section. The radial passage into theneighboring flow space enables axial outflow from the filter element,only closed at the intake side by the curved connecting section, whilethe outflow side is axially open.

According to an advantageous embodiment it is provided that the spacersor a part of the spacers are in the form of adhesive traces, forexample, glue beads or adhesive dots, by means of which the neighboringfilter layers are adhesively connected. The adhesive traces thereforefulfill a dual purpose. On the one hand, they connect neighboringparallel extending filter layers with one another, on the other hand,they keep the filter layers at the desired spacing relative to oneanother, so that a corresponding flow space with desired dimension isformed. Optionally, the adhesive traces are combined with other,non-adhesive spacers that are embodied either as separate components or,for example, are generated by embossment of the filter web in adirection transverse to the axial direction.

The entire filter element is comprised preferably of precisely onecontinuous filter web that is folded to form the filter layers, whichhas advantages in particular with regard to manufacturing-technologicalaspects. For example, it is possible to apply onto a flexible filter webat least two parallel extending adhesive traces and to subsequently foldthe filter web to a plurality of parallel extending filter layers sothat the adhesive traces are located between two neighboring filterlayers and adhesively connect them.

With regard to the outer dimensions the filter element has aparallelepipedal shape wherein opposed end faces of the parallelepipedform the intake and outflows sides.

According to a further aspect of the invention, the filter element iscylindrically designed and has a plurality of concentrically arrangedfilter cylinders or is spirally wound, wherein the filter cylinders eachare comprised of filter material wherein between neighboring filtercylinders spaces are provided and the intermediate spaces betweenneighboring filter cylinders provide flow spaces for the fluid. In orderto prevent that the unfiltered fluid that is supplied axially at oneside is guided without filtration to the opposite end face, the flowspaces between the filter cylinders are expediently alternatingly openat one axial end face and closed at the opposite end face, respectively.This is done, for example, in such a way that immediately neighboringflow spaces that are concentrically positioned relative to one anotherare open or closed at the axial intake side and, correspondingly, areclosed or open at the opposite outflow side. In this way, it is ensuredthat fluid flowing into the filter element must pass radially the wallof the neighboring filter cylinders within the flow spaces in order toreach the neighboring flow space from where axial outflow is possible.

According to an expedient embodiment, between the concentric filtercylinders spacers are provided that are embodies as adhesive strips. Inprinciple, it is possible to provide exclusively adhesive strips asspacers or a combination of adhesive and non-adhesive spacers.

In all aforementioned filter devices, advantageously sealing rings areprovided between the filter element and the inner side of the filterhousing that separate the unfiltered side from the filtered side of thefilter element in question. The sealing ring is preferably locatedadjacent to the outflow side and in particular at the transition betweenthe outer wall surface of the filter element and the axial end face inthe outflow area. This configuration makes it possible to also utilizethe outwardly positioned wall surface as a flow side in particular forintake of the unfiltered fluid. The force loading of the sealing ring isrealized preferably in the axial direction but optionally also anexclusive or additional radial loading of the sealing ring can beexpedient.

The sealing ring extends in radial direction advantageously up to theouter wall surface of the filter element; it thus does not projectradially. According to a further embodiment it can be expedient howeverthat at least one section of the sealing ring radially projects past theouter wall surface of the filter element.

Advantageously, the filter element, independent of its constructiveembodiment, is to be radially inserted into the filter housing by meansof a housing opening that is to be closed by a lid and is to be flownthrough axially by the fluid to be filtered. Moreover, it can beexpedient to arrange upstream of the filter element a prefilter that isembodied in particular as a cyclone preseparator and is expediently alsoflown through in the axial direction. Moreover, according to a furtheradvantageous embodiment, a secondary or fine filter element can bearranged downstream of the filter element and, advantageously, it isalso flown through in the axial direction. In combination with theprefilter, one thus achieves as a whole an axial flow through threefilter units. The downstream fine filter element is preferably insertedlike the main filter element radially through the closable housingopening into the filter housing. As a fine filter element, block-shapedelements are suitable, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and expedient embodiments are to be taken from theadditional claims, the Figure description, and the drawings. It is shownin:

FIG. 1 a perspective illustration of a filter device that is used inparticular as an air filter for internal combustion engines andcomprises axially sequentially arranged a cyclone preseparator, a mainfilter element, and a downstream fine filter element, wherein the mainfilter element is embodied as a double bellows filter with two radiallynested filter bellows;

FIG. 2 the filter device according to FIG. 1 in a different perspective;

FIG. 3 the main filter element of the filter device of FIG. 1 or 2 insection;

FIG. 4 a perspective view of the star-shaped filter folds of a mainfilter element;

FIGS. 5 and 6 a filter device analog to FIG. 1 or 2 but with analternative embodiment of the main filter element that is comprised oftwo radially nested filter bellows that are joined in the area of theaxial intake side;

FIG. 7 the filter element of FIG. 5 or 6 in section;

FIGS. 8 and 9 a further embodiment of a filter device with cyclonepreseparator, main filter element, and downstream fine filter element,wherein the main filter element is embodied as a parallelepipedalelement and is comprised of a continuous filter web with a plurality ofparallel filter layers that are connected to one another by curvedconnecting sections;

FIG. 10 the main filter element of FIGS. 8 and 9 in a perspectiveindividual illustration;

FIG. 11 an enlarged illustration of the detail XI of FIG. 10;

FIG. 12 an enlarged illustration of the detail XII of FIG. 10;

FIGS. 13 and 14 yet another embodiment of the filter device with cyclonepreseparator, main filter element, and downstream fine filter element,wherein the main filter element comprises a plurality of concentricallyarranged filter cylinders of filter material between which spacers areprovided wherein the intermediate spaces between the filter cylindersprovides flow spaces for the fluid;

FIG. 15 the main filter element of FIG. 13 or 14 in a perspectivesection illustration;

FIG. 16 an enlarged detail view of the detail XVI of FIG. 15;

FIG. 17 an enlarged detail view of the detail XVII of FIG. 15.

In the Figures, same components are provided with same referencenumerals.

EMBODIMENT(S) OF THE INVENTION

The filter device 1 illustrated in FIGS. 1 and 2 is an air filter for aninternal combustion engine comprised of a filter housing 2 in which amain filter element 7 is received, a cyclone preseparator 6 as aprefilter, as well as a downstream fine filter element 10. The filterhousing 2 has at its circumferential wall an opening which is covered bya closable lid 3 that is arranged detachably by means of closureelements 4. By means of this opening in the wall surface of the filterhousing the main filter element 7 and expediently also the fine filterelement 8 can be inserted into or removed from the receiving spacewithin the filter housing 2 radially or transversely to the axialdirection. The main filter element 7 is positioned immediately below thelid 3, the downstream fine filter element 8 is positioned howeveraxially displaced in a projection of the filter housing so that forinsertion of the fine filter element 8 it must first be radiallyinserted into the filter housing 2 with the lid in the open position andsubsequently axially moved into the projection.

The cyclone preseparator 6 is also located in a projection which isformed integrally with the filter housing 2. In the cyclone preseparatorthe dirt particles are transported outwardly away from the axiallysupplied air by centrifugal force in a rotating air flow and separated.By means of a removal opening 9 in the filter housing that is directeddownwardly, the dirt particles that have been separated in the cyclonepreseparator can be removed from the filter housing. Optionally, theprojection in which the cyclone preseparator is received is embodied asa separate component that is connected to the filter housing.

Preseparator 6, main filter element 7, and fine filter element 8 arepositioned axially sequentially behind one another and have the samelongitudinal axis 5 which at the same time is the longitudinal axis ofthe entire filtering device 1. The fluid to be filtered flows through inaxial direction according to the illustrated arrows.

The main filter element 7 is comprised of two individual radially nestedfilter bellows 10 and 11 wherein the outer filter bellows 10 iscylindrical and the inner filter bellows 11 is conical and tapers in theflow direction but has a uniform fold width. Between the inner side ofthe outer filter bellows 10 and the outer side of the inner filterbellows 11 there is a flow space 12 that, as a result of the deviatingshape of the two filter bellows 10 and 11, in axial direction has achanging cross-section. Since the inner filter bellows 11 tapers in theflow direction, the flow space 12 has accordingly a cross-section thatincreases in the flow direction.

A support frame 13 frames the flow space 12 and supports the two filterbellows 10 and 11 relative to one another and provides additionalstability to the entire filter element 7. The flow space 12 is closedoff at the axial intake side which can be achieved in that at this sidea cover ring 15 is arranged which covers the axial end face of theradially inwardly positioned filter bellows 11 and additionally also thenarrow gap at the flow space 12 at this side. As best seen in FIG. 3,the cover ring 15 preferably completely covers the filter media folds atthe end face of the inwardly positioned filter bellows 11. Again asshown in FIG. 3, the cover ring 17 preferably completely covers thefilter media fold at the opposing end face of the outwardly positionedfilter bellows 10. However, it can also be expedient to join the twofilter bellows 10 and 11 at the intake side of the main filter elementto such an extent that no flow gap relative to the intake side isprovided. In this case, it is sufficient to arrange the cover ring 15only at the axial end face of the inner filter bellows 11 although thecover ring 15 may cover axial end faces of filter bellows 10 and 11.

The prefiltered fluid from the cyclone preseparator 6 is suppliedaxially to the end face intake of the main filter element 7. A portionof the fluid flows immediately axially into the interior 14 of the innerfilter bellows 11 that is closed relative to the outflow side by a coverdisk 16. The cover disk 16 extends radially only across the opening ofthe interior 14 so that the fluid in the interior 14 is prevented fromflowing out axially by the cover disk 16 and instead must flow radiallythrough the wall of the inner filter bellows 11 and farther into theflow space 12 between the filter bellows 10 and 11 that represents aclean chamber for the fluid filtered by the main filter element 7.

A second partial flow of the fluid supplied to the main filter element 7passes immediately through the axial end face or intake side into theradially outwardly positioned filter bellows 11 that is closed off atthe opposite axial outflow side so that the incoming fluid flowsradially inwardly into the flow space 12 that is open toward thefiltered side of the main filter element 7 so that the filtered fluidcan flow axially out of the flow space 12. A further partial flowreaches the radially outwardly positioned wall surface of the outwardlypositioned main filter element 10 and flows radially through it from theexterior to the interior into the flow space 12.

As illustrated in FIGS. 1 and 2 and in particular in the enlargedillustration of the filter element 7 according to FIG. 3, the axial endface of the radially outwardly positioned first filter bellows 10 in thearea of the filtered side or outflow side is covered by a cover ring 17that prevents axial outflow of the fluid so that the fluid at the outerbellows 10 is forced to flow radially from the exterior to the interiorinto the flow space 12.

A connecting flange 18 is integrally formed with the cover ring 17 andis located at the radial outer side of the radial outer filter bellows10 in the area of the outflow side and delimits and supports a sealingring 19 that is clamped at the outflow side axially between theconnecting flange 18 and the housing component of the filter housing.This sealing ring 19 separates the unfiltered side from the filteredside of the filter element 7. The sealing ring 19 has a U-shaped profilewherein the open U-side is pointing radially outwardly. The sealing ring19 is located immediately at the outflow side or the end face of thefilter element 7 and extends in the radial direction outwardly,substantially beginning at the radially outwardly positioned wallsurface of the outer filter bellows 10. It can be expedient that thesealing ring 19 extends also at least partially across the axial endface at the outflow side and thus has at the inner side a smallerdiameter than the diameter of the filter bellows 10 at the radiallyoutwardly positioned wall surface.

In the mounted position the sealing ring 19 is axially loaded. It canalso be expedient to additionally load the sealing ring 19 in the radialdirection.

As is shown in FIG. 4, the two filter bellows 10 and 11 each areconfigured as a star-shaped folded filter whose folds are adhesivelyconnected in the area of one end face. For this purpose, adhesive layers20 and 21 are applied in the area of the end faces onto the individualfolds of each filter bellows in order to adhesively connect two folds toone another that are immediately contacting one another. The radiallyoutwardly positioned filter bellows 10 has such an adhesive layer 20 atthe intake side; the radially inwardly positioned filter bellows 11 hasa corresponding adhesive layer 21 in the area of the outflow side. Theadhesive connection has the result that two immediately neighboringfolds each are glued together and between two pairs of glued-togetherfolds in the axial direction of the longitudinal axis 5 a flow passageis formed that extends across the axial length of each filter bellows.This has the effect that, as illustrated in FIG. 3, the supplied fluidflows axially across the glued-together front edges of the radiallyoutwardly positioned filter bellows 10 along the axial flow passageswhile in the radially inwardly positioned filter bellows 11 an axialoutflow is possible through the front edge provided with the adhesivelayer 21 in the outflow area

In FIG. 4 a filter bellows 10 or 11 in the form of a star-shaped filteris illustrated during the manufacturing process. On only one side of thefolds an adhesive bead 20 or 21 is applied so that upon adhesivelyconnecting immediately neighboring folds two layers are positioned ontop one another and are glued together by means of the adhesive beads.On the side of the folds opposite the adhesive beads 20, 21 acorresponding adhesive layer is not used so that at this side axial flowpassages are formed.

The embodiments according to FIGS. 5 to 7 correspond substantially tothe first embodiment illustrated in FIGS. 1 through 4 so that withrespect to matching features reference is had to that description. Themain filter element 7 also comprises two filter bellows with a radiallyoutwardly positioned filter bellows 10 and a radially inwardlypositioned filter bellows 11 which however in contrast to the firstembodiment are not two separate components but are a common componentjoined at the end face. The outer filter bellows 10 has a cylindricalbasic shape, the inner filter bellows 11 a conical shape so that theintermediately positioned flow space 12 widens in the axial directiontoward the outflow side with regard to cross-section. At the outflowside the inner filter bellows 11 is closed off fluid-tightly by coverdisk 16. The outer filter bellows 10 is also covered at the outflow sidein a fluid-tight way by a cover ring 17. Between the cover disk 16 andthe radially surrounding cover ring 17 there is an annular gap by meansof which the flow space 12 communicates with the outflow side or thefiltered side.

At the intake side the outer filter bellows 10 and the inner filterbellows 11 have a common front edge where the individual folds of eachfilter bellows are joined at this front edge. With regard tomanufacturing technology, this can be achieved, for example, in thatfolds in a star shape with front edges in axial direction are embossedinto a cylindrical folded filter paper and subsequently a part of thefilter cylinder is turned over so that two radially nested filterbellows are formed.

The intake is realized across the entire axial end face that iscomprised of the two filter bellows 10 and 11. Outflow is realized onlythrough the annular flow opening between the cover disk 16 and coverring 17.

in FIGS. 8 through 12 a further embodiment of a filter device forfiltration of gaseous fluids, in particular combustion air for internalcombustion engines, is illustrated. As in the preceding embodiments, thefilter device 1 according to FIGS. 8 and 9 is comprised of a filterhousing 2 with a laterally inserted main filter element 7 that hasupstream thereof in axial flow direction a prefilter 6 that is embodiedas a cyclone preseparator and which has arranged downstream in the axialdirection a fine filter element 8. The flow direction of air filterunits is axial without reversal or deflection of the flow direction.

In FIG. 10 through 12 the main filter element 7 is shown in detail. Thefilter element 7 is comprised of a continuous filter web 22 that is laidor folded to a plurality of filter layers 22 a that extend parallel toone another and are spaced relative to one another. As a whole, thefilter element 7 has a parallelepipedal shape. Between two neighboringfilter layers 22 a there are flow spaces or passages in which the fluidcan flow axially. As a result of the unitary configuration withexpediently only a single filter web 22, the individual filter layers 22a are connected to one another by curved connecting sections 24 whichare also a unitary component of the filter web 22. In this way, at theintake side of the filter element 7 intake openings to the flow passagesbetween parallel filter layers 22 a result which, however, at theoutflow side are closed by a connecting sections 24 a of the filter webso that the incoming unfiltered fluid cannot axially escape but mustflow radially through the neighboring filter layers. Subsequently, thefluid passes into neighboring flow spaces 12 that represent cleanchambers and are closed by curved connecting section 24 in the area ofthe axial intake side, but at the axial outflow side are open so thatthe filtered fluid can flow out axially at this side out of the filterelement 7.

The filter layers 22 a are spaced apart by means of adhesive strips 23that have the function of spacers and also glue together neighboringfilter layers. Advantageously, across the width of the filter element aplurality of parallel extending adhesive strips 23 are arranged betweentwo neighboring filter layers 22 a. Between two parallel adhesive strips23 there is a passage-shaped flow space. Across the entire width of thefilter element in this way several parallel extending flow passages orspaces are formed between two filter layers 22 a.

For producing the filter element 7, at least two parallel extendingadhesive strips or beads are applied on a flexible continuous filterweb, in particular expediently onto both sides of the filter web.Subsequently, the filter web is folded to form several filter layerswherein the adhesive strips connect the parallel extending filter layersand at the same time support them.

It can be expedient to provide additional spaces that optionally arenon-adhesive.

A further embodiment of a filter device 1 for filtration of gaseousaxial fluids is illustrated in FIGS. 13 to 17. In this embodiment thefilter device 1 is also of a three-part configuration and comprises aprefilter 6, a main filter 7, and a fine filter element 8 wherein allfilter units are flown through in the axial direction in the samedirection and the main filter element 7 as well as the fine filterelement 8 are to be inserted radially into the filter housing 2 when thehousing lid 3 is open.

As can be seen in the individual illustration of the filter element 7according to FIGS. 15 to 17, the filter element is cylindrical andcomprises a plurality of concentrically arranged individual filtercylinders 25 wherein two immediately neighboring filter cylinders 25 arepositioned at a spacing to one another so that between the filtercylinders 25 a flow space is provided, respectively. As can be seen inthe enlarged illustration according to FIGS. 16 and 17, these flowspaces that extend in the axial direction are closed off at the axialend face of the filter element and are open at the opposite end face ofthe filter element. Two flow spaces each that are positioned in theradial direction immediately adjacent to one another are closed or openat different axial end faces. In this way, flow spaces or passages areformed, on the one hand, that are closed at the intake side and open atthe outflow side and through which the filtered fluid can flow out. Onthe other hand, intake passages 26 are formed that are open at theintake side and are closed at the outflow side. The incoming unfilteredfluid at this side cannot flow out axially through the intake passages26 but the unfiltered fluid must radially pass through the walls of thefilter material of neighboring filter cylinders and then flow axiallyout through the flow spaces 12 that represent the clean chambers.

Two immediately neighboring filter cylinders 25 are connected at the endface by connecting sections 24 with one another, respectively, whichsections are however expediently embodied as a component separate fromthe filter cylinders 25 and are connected to the end faces of tworadially neighboring filter cylinders. The connecting sections 24 thushave an annular shape. The connecting sections 24 connect, for example,at the intake side, two radially immediately neighboring filtercylinders 25 with one another wherein radially inwardly and radiallyoutwardly a gap adjoins, respectively, in order to form an intakepassage for the unfiltered fluid. At the outflow side the connectingsections 24 are displaced relative to the connecting sections at theintake side radially by one filter cylinder, respectively, so that theintake passages at the outflow side are closed and at the same time theflow passages for removing the filtered fluid are closed at the intakeside and open at the outflow side.

In addition, spacers 23 a are provided by means of which the individualfilter cylinders 25 are spaced apart from one another and fixed. Asshown in FIG. 15, across the axial length of the filter element 7 aplurality of individual preferably annularly designed spacers 23 a arearranged wherein expediently at one axial position several spacers 23 aare positioned between two filter cylinders 25, respectively. Atdifferent axial locations the spacers 23 a, in accordance with theconnecting sections 24 at the end faces, can be arranged between twofilter cylinders, respectively, wherein expediently a spacer 23 a isinserted only into every other intermediate space, viewed in radialdirection, between neighboring filter cylinders, respectively. Ataxially different locations spacers 23 a are inserted into every othergap between the filter cylinders such that, as a whole, i.e., across theentire axial length of the filter element, each intermediate spacebetween neighboring filter cylinders is provided with spacers at leastatone axial position.

The spacers 23 a can be embodied as adhesive strip sections andadditionally to their supporting function can also take on an adhesivefunction. At the same time, it is also possible to employ non-adhesivespacers.

According to a modified embodiment the filter element 7 illustrated inFIGS. 13 to 17 is comprised of a spirally wound filter web that iseither provided with flat walls or has folds. By means of spacers and/orclosure or cover elements the axial flow passages in the filter elementare closed partially at the outflow side and partially at the intakeside wherein the opposite end face of a flow passage, respectively,remains open so that the filter material of the filter element and canbe radially flown through by the introduced fluid.

The invention claimed is:
 1. An air filter element for exchangeableinstallation in a filter housing in which the filter element is flownthrough by a fluid to be filtered, the filter element comprising: afluid flow intake side; a fluid outflow side; wherein said outflow sideis spaced apart axially from said inflow side; at least two radiallynested filter bellows; wherein at least one filter bellows of said atleast two filter bellows is to be flown through in a radial direction;wherein an annular flow space is formed radially between said nestedfilter bellows, said annular flow space in fluid flow communication withan end face of the filter element; wherein each filter bellows isembodied as a star-shaped filter with filter folds arranged in a starshape; a sealing ring arranged on at least one end face of said filterelement, said sealing ring operable for engaging an interior of saidfilter housing to separate an unfiltered side from a filtered side ofsaid filter element; wherein a cover disk closes over an interior of aradially inwardly one of said nested filter bellows, said cover diskextending radially across said interior preventing fluid in the interiorfrom flowing axially by said cover disk; wherein front edges of filtermedia folds of a first one of said at least two filter bellows at oneend face are completely covered by a cover ring; wherein front edges offilter media folds of said at least two filter bellows are completelycovered at an opposite end face with a second cover ring preventingaxial flow from passing through filter media fold front edges at saidopposite end face; wherein a portion of said filter folds of one of saidat least two filter bellows is immediately contacting against andadhesively connected and tacked to immediately neighboring filter foldsof a different one of said at least two filter bellows at an axial endface of said filter bellows.
 2. An air filter element for exchangeableinstallation in a filter housing in which the filter element is flownthrough by a fluid to be filtered, the filter element comprising: afluid flow intake side; a fluid outflow side; wherein said outflow sideis spaced apart axially from said inflow side; at least two radiallynested filter bellows; wherein at least one filter bellows of said atleast two filter bellows is to be flown through in a radial direction;wherein an annular flow space is formed radially between said nestedfilter bellows, said annular flow space in fluid flow communication withan end face of the filter element; wherein each filter bellows isembodied as a star-shaped filter with filter folds arranged in a starshape; a sealing ring arranged on at least one end face of said filterelement, said sealing ring operable for engaging an interior of saidfilter housing to separate an unfiltered side from a filtered side ofsaid filter element; wherein a cover disk closes over an interior of aradially inwardly one of said nested filter bellows, said cover diskextending radially across said interior preventing fluid in the interiorfrom flowing axially by said cover disk; wherein front edges of filtermedia folds of a first one of said at least two filter bellows at oneend face are completely covered by a cover ring; wherein front edges offilter media folds of said at least two filter bellows are completelycovered at an opposite end face with a second cover ring preventingaxial flow from passing through filter media fold front edges at saidopposite end face; wherein front edges of the filter folds of at leastone of said filter bellows are tacked closed at at least one of saidintake side or said outflow side of said filter element, ensuring fluidflow of said filter bellows must flow radially through said tackedfilter bellows in radial direction and not through said tacked frontedges.
 3. The filter element according to claim 2, wherein a free flowpassage is formed between two tacked filter folds each at the end faceof a filter bellows.
 4. The filter element according to claim 2, whereinsaid tacked filter folds are glued together.
 5. Filter element accordingto claim 2, wherein the filter bellows are embodied as individualbellows.
 6. The filter element according to claim 2, wherein a radiallyinwardly positioned one of said at least two filter bellows is conicallyembodied, wherein a radially outwardly positioned one of said at leasttwo filter bellows is cylindrically embodied, wherein said flow spacebetween said nested filter bellows has a cross-section that increasestowards said outflow side of said filter element, wherein said flowspace between said filter bellows is framed by a support frame, saidsupport frame cross-section increasing towards said outflow side of flowspace between said nested filter bellows such that said support frame onopposing sides supports respective ones of said radially nested filterbellows in position relative to one another and frames the flow space.7. The filter element according to claim 2, wherein said flow spacebetween said nested filter bellows has a cross-section that increasestowards said outflow side of said filter element.
 8. The filter elementaccording to claim 2, wherein said flow space between the filter bellowsis framed by a support frame such that said support frame on opposingsides supports respective ones of said radially nested filter bellows inposition relative to one another and frames said flow space.
 9. Thefilter element according to one of the claim 7, wherein said flow spaceforms a clean chamber and is closed off axially relative to said intakeside wherein said filter bellows that radially delimit said flow spaceare each are flown through radially in said direction of the flow space.10. The filter element according to claim 9, wherein at least one ofsaid filter bellows at one end face of said filter element is open foraxial flow into said filter media folds.
 11. The filter elementaccording to claim 2, wherein said annular flow space formed betweensaid radially spaced nested filter bellows is open for flow at eithersaid intake side or said outflow side of the filter element and isclosed off to flow at the opposing flow side of the filter element,wherein said annular flow space is open only to one of said flow sidesof the filter element.
 12. The filter element according to claim 11,wherein said second cover ring is arranged at said closed off flow sideconnecting adjacent axial end faces of said nested filter bellows.